In recent memory hard disk drives, high storage capacity and miniaturization have been demanded. In order to increase the recording density, it has been strongly urged to lower the flying height of a magnetic head and to reduce the unit recording area. Along with this trend, the surface qualities required after polishing have become severely assessed every year even in a manufacturing step for a substrate for a magnetic disk. In order to satisfy the lowering of flying height of the magnetic head, the surface roughness, the microwaviness, the roll-off and projections are required to be reduced, and in order to satisfy the reduction in unit recording area, the acceptable number of scratches per one side of the substrate has been reduced, and the sizes and depths of the scratches have become increasingly smaller.
Also, in the field of semiconductors, highly integrated circuits and higher speed at the operating frequencies have been advanced, and the production of thinner wiring is required especially in highly integrated circuits. As a result, in the method for manufacturing a substrate for semiconductors, since the focal depth becomes more shallow with the increase in resolution required for an exposure device during the exposure of a photoresist, even more improvement in surface smoothness and planarization is desired.
In order to meet the above requirements, a polishing composition for reducing surface roughness (Ra, Rmax), scratches, pits, projections and the like, and improving surface planarization has been proposed (JP-A-Hei-9-204657, JP-A-Hei-11-167715, and JP-A-Hei-11-246849), in which the problem of “micro scratches” (which are scratches having a broad width and very shallow depth (depth of 0.1 nm or more and less than 5 nm, width of 10 μm or more and less than 50 μm, and length of 10 μm or more and less than 1000 μm)) has been solved by adding a finishing polishing step with colloidal silica. In addition, a polishing composition for the purpose of reducing micro scratches has been proposed (JP2003-155471 A, and JP2003-147337 A).
In addition, for the purposes of an increase in the polishing rate and a reduction of surface defects, a polishing composition in which a fumed metal oxide and an abrasive such as colloidal silica are mixed has been disclosed (WO 2001-36554).